C++ 中奇怪的标准输出行为
我希望我的程序在处理时显示 unix 风车。 有一个 for 循环，并且在每次迭代中都有一个 printf 函数：
printf("Fetching articles (%c)\r",q);
q 是风车中的字符之一 (-\|/)，具体取决于迭代次数。
问题是 - 看起来在 100 次迭代中，显示的行只有两次变化，并且每次迭代大约需要一秒钟才能完成。
这可能是什么原因造成的？
这是整个循环，风车只有两个可能的字符：
for (int i=0;i<numb_articles;i++) {
memset(file_path,0x0,BUFF_SIZE);
url=article_urls[i];
if (rules->print!=NO_PRINT) {
url=modify_url(url,rules->printout,rules->print);
if (url=="NULL")
continue;
}
get_page(url,file_content);
if (strcmp(rules->save.data(),"NULL")!=0)
if (!check_save(rules->save,file_content,url))
continue;
at_least_one_saved=true;
numb_articles_accepted++;
encoding_list[i]=get_encoding(file_content);
title=get_title(file_content,err_msg);
if (title=="")
continue;
title_list[i]=strdup(title.data());
filename=get_filename(title);
int count=numb_fn_found(filename_list,i,filename.data());
char *tmp = new char[10];
if (count>0) {
sprintf(tmp,"(%d)",count);
filename.insert((size_t)filename.length(),tmp);
}
filename_list[i]=strdup(filename.data());
char q;
if (i%2==0)
q='|';
else q='-';
printf("Fetching articles (%c)\r",q);
ofstream output_file;
sprintf(file_path,TMP_FILE,filename.data());
strncat(file_path,".html",5);
output_file.open(file_path);
output_file << file_content;
output_file.close();
}
I want my program to display the unix windmill while processing. There's a for loop and in every iteration theres a printf function:
printf("Fetching articles (%c)\r",q);
q is one of the characters in the windmill (-\|/) depending on the iteration number.
The problem is - it seems like in 100 iterations there are only two changes in displayed line, and every iteration takes about one second to complete.
What could be the aouse for this?
Here's the whole loop with only two possible chars for the windmill:
for (int i=0;i<numb_articles;i++) {
memset(file_path,0x0,BUFF_SIZE);
url=article_urls[i];
if (rules->print!=NO_PRINT) {
url=modify_url(url,rules->printout,rules->print);
if (url=="NULL")
continue;
}
get_page(url,file_content);
if (strcmp(rules->save.data(),"NULL")!=0)
if (!check_save(rules->save,file_content,url))
continue;
at_least_one_saved=true;
numb_articles_accepted++;
encoding_list[i]=get_encoding(file_content);
title=get_title(file_content,err_msg);
if (title=="")
continue;
title_list[i]=strdup(title.data());
filename=get_filename(title);
int count=numb_fn_found(filename_list,i,filename.data());
char *tmp = new char[10];
if (count>0) {
sprintf(tmp,"(%d)",count);
filename.insert((size_t)filename.length(),tmp);
}
filename_list[i]=strdup(filename.data());
char q;
if (i%2==0)
q='|';
else q='-';
printf("Fetching articles (%c)\r",q);
ofstream output_file;
sprintf(file_path,TMP_FILE,filename.data());
strncat(file_path,".html",5);
output_file.open(file_path);
output_file << file_content;
output_file.close();
}
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写入每一行后刷新输出：
如果不这样做，通常会对 stdout 进行缓冲，并且仅在看到换行符或其内部缓冲区已满时才转储其输出。
Flush the output after writing each line:
Without doing this, normally
stdoutis buffered and only dumps its output when a newline is seen, or its internal buffer fills up.输出（控制台）被缓冲。 也就是说，它仅在缓冲区已满或写入换行符时才将输出写入屏幕。 如果您想一次输出一个字符，则需要显式调用 fflush(stdout) 来刷新输出缓冲区。
The output (console) is buffered. That is, it only writes the output to the screen when the buffer is full or a newline is written. If you want to output characters one at a time, you will need to call
fflush(stdout)explicitly to flush the output buffer.